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Heart-Stoppers

Galapagos marine iguana

The marine iguanas of the Galapagos are remarkable in their unlizard-like ability to forage for vegetation and other tidbits underwater. These iguanas make good eating, and they are at risk along the rocky shores of the Galapagos. But the marine iguanas have special card to play when approached by sharks armed with their supersensitive hearing. The iguanas voluntarily stop their hearts from beating. Otherwise, sharks as far away as 3-4 meters can home in on their heartbeats. Amazingly, marine iguanas can survive up to 45 minutes without functioning hearts. This represents a remarkable evolutionary adaptation in the perpetual warfare between prey and predators.

But, to the west across the Pacific, in Indonesia, another reptile, the fear-some Komodo dragon, can also voluntarily stop its heart. Komodo dragons have no sharks to fear. In fact, they are the top predators on the islands they inhabit, dining on deer and, rarely, a human or two. Was this a purposeful adaptation? If so, to what threat?